Numerous methods are available for producing food products and biodegradable polymers. In the case of foods, these methods may be categorized generally as static (still) or dynamic methods. Static methods may be defined as those in which a batch of constituents is disposed in a cooking vessel and allowed to remain still or free of movement while being cooked, such as in an oven baking process or pressure moulding or baking process. These include processes in which the batch of material is caused to move on a conveyor through a cooking apparatus, such as a baking tunnel. Here the constituents would remain still in relation to the surface or vessel on or in which they were being transported.
Dynamic processes are those in which a quantity of constituents is fed into an apparatus—whether in a continuous or semi-continuous stream or batchwise—in which mechanical energy is imparted to these constituents to cause relative movement within the batch or stream while energy is absorbed to cause cooking. Such movement could include active or passive mixing. One dynamic thermal treatment method is extrusion, where constituents are caused to mix with each other while shear is being imparted within the extruder barrel. Extrusion can be used to produce a variety of food or edible products. The internal shear forces generated within the apparatus provide a substantial portion of the heat that is used for cooking the constituents. These products can be designed for human or animal consumption, or both. Another dynamic cooking method makes use of a continuous mixer to cause relative internal movement of the constituents while thermal energy is applied to result in cooking.
With respect to pets, a variety of food products is available. Some of these products are produced through extrusion. Certain extruded products are designed to extend the duration of chewing by a pet, especially dogs, with the goal of providing a product with which pets can chew and enjoy. Pet owners often rate the value of a pet food product or pet snack by its chewing duration. “One bite and it is gone” is a frequent complaint of owners of large dogs, for example.
Products that facilitate extended chewing can help improve dental hygiene and reduce periodontal disease, which is a widespread problem for pet cats and dogs. This is because the natural diet of animals in the wild includes many foods that require extended chewing before the pieces are small enough to be swallowed, contributing to dental hygiene and facilitating digestion. In contrast, the diet of domesticated pets frequently lacks naturally chewy foods, depriving them of the above benefits.
Conventional food processing methods often do not produce products that have textures comparable to naturally chewy foods. Certain attempts have been made, however, to produce pet products having an extended chewing duration. But, most of these products have disadvantages.
Some are simply not edible. When the pets chew or break up and swallow these products, they suffer digestive problems. Some pass undigested through the pet and can contribute to diarrhea and increased fecal volume. Most pet owners want to reduce fecal volume, diarrhea and soft stools. Even some products that claim to be made from edible constituents are not edible in final form, because of processing that fails to ensure digestibility.
European patent application number EP 0 552 897 A1 discloses an edible animal chew product with a flexible cellular matrix containing cellulosic fibers, e.g., 20 to 50% corncobs and oral care additives. Corncobs and cellulosic materials are not readily digestible and can also contribute to diarrhea and increased fecal volume.
There are nevertheless chewy products that are formulated with digestibility in mind. However, some of these prior art chewy products are high in calories. It is desirable that such products therefore be fed as treats or snacks to comprise only a small portion of the pet's diet, so as not to create a dietary imbalance.
A further problem with some prior art chewy products is production cost. Certain chewy products are formulated with pliable materials that are designed to resist the pet's chewing force. The pliable materials tend to be expensive. Attempts to mix pliable materials and less expensive materials have created a complex balancing system in which it is often difficult to ensure that the less expensive materials do not compromise the strength and integrity of the more expensive pliable materials.
Still another problem with certain prior art highly resistant chewable products is safety. For example, one prior art chewable pet toy has a protein based thermoplastic composition with protein levels between 50-70%. High protein products, including those fabricated from refined high protein constituents, are not only expensive but may bring potential danger as well. Some experts believe that high protein levels can contribute to renal failure and to blockage of the urinary tract in pets consuming same.
Some prior art products attempt to increase chewing duration by increasing the rigidity of the product. Certain of these products are virtually rock hard. These products can chip or break a pet's teeth. For example, one such product requires an operating pressure above 10 MPa to break. Many of the harder products of the prior art are glassy in nature and have a tendency to shatter into sharp, hard fragments when bitten. These fragments can lodge in the animal's throat or injure its mouth. This is especially a problem with products produced by high pressure injection molding techniques.
Product design also plays an important role in producing a product that is safe and has a long chewing duration. For example, some non-glassy products of the prior art may not shatter, but may be poorly designed, causing extensive bleeding of the gums when chewed. In part, one of the problems of prior art chewy food products is that they have a limited range of textures to choose from, culminating in products having a texture that causes bleeding of the gums.
Furthermore, the textures of many chewy products are often unappealing and unpalatable. For example, extruded dry pet foods are typically provided in hard lumps and have a dry, dusty appearance. They can be inconvenient for the consumer to handle. Still further, some prior art products are unstable, so that their texture changes with time and they lose desirable characteristics.
Some prior art chewy products are based on starch. Converting starch-based materials into solid articles is known. However, the injection molding equipment that is typically used to convert such starch-based materials is expensive and complex to operate and known methods of solidifying starch-based materials provide a limited range of textures.
Extruding food constituents at low water activities, although known, has until now been fraught with difficulty. The constituents required for such extrusion were often expensive and produce a limited range of textures. When processing and cooking food, bio-polymers, such as starch and proteins, unravel first and then recombine, forming a desired structure, e.g., a biscuit shape. If this unraveling and recombination is restricted or interrupted, the resulting products have little binding and are relatively weak. Unraveling can only occur in the liquid phase and is facilitated by hydration of the unfolding polymers.
At low water activities there is little water available. These systems hence have limited hydration potential. Conventional extrusion processes are therefore operated at high water activity levels, wherein a large amount of water is added to facilitate hydration. The large amount of water necessitates energy-intensive and environmentally unfriendly post-extrusion drying or the adding of acid and other preservatives. This often has undesirable consequences for the products; for example, the water restricts the range of textures that can result.
Extrusion of pet foods is typically conducted at high moisture levels, e.g., approximately 26% moisture, and high water activities, e.g., aw greater than 0.95. However, these parameters are too high to produce the textures needed for products of extended chewing duration. The water activity for extended chewing products has typically been less than 0.65, with moisture contents of about 7.0% to 17% and with 10% to 20% of total solvent by weight. At these water activities, however, if the methods of the prior art are used, there is insufficient water for hydration, and it is necessary to cook at very high temperatures and pressures or for extended periods, which frequently results in high levels of starch damage and/or burning of the products.
A need therefore exists for improved food products that can provide a long chewing duration, are edible and have improved textures and for methods of producing same.
A need exists too for a polymeric material that can offer structural integrity suitable for use in manufacturing load-bearing items, such as furniture, supporting devices and containers.
A need exists too for a means of operating a processing facility for producing substantially dry products with reduced environmental emissions.